There has been known a vacuum type water supply system which supplies water by utilizing vacuum suction. As one example of the vacuum water supply system, there is a vacuum type sewage line system. The vacuum type sewage line system is provided with a vacuum station, a vacuum sewage pipe, and a vacuum valve unit.
The vacuum station is provided with a vacuum pump, a water collection tank, and a pressure pump. In the vacuum sewage pipe, its upstream side is connected to a vacuum valve unit, and its downstream side is connected to the water collection tank of the vacuum station. The vacuum pump of the vacuum station generates a negative pressure within the vacuum sewage pipe. Due to this negative pressure within the vacuum sewage pipe, waste water within the vacuum valve unit is drained to the water collection tank of the vacuum station through the vacuum sewage pipe. The waste water reserved in the water collection tank is fed further downstream by the pressure pump.
The vacuum valve unit is provided with a water storage basin which temporarily reserves the waste water fed from the upstream side. The vacuum valve is interposed between a water suction pipe which lower end is positioned within the water storage basin, and the vacuum sewage pipe. The vacuum valve shuts off communication between the water suction pipe and the vacuum sewage pipe when the valve is closed, and allows communicates between the water suction pipe and the vacuum sewage pipe when the valve is open so as to supply the waste water within the water storage basin to the vacuum sewage pipe.
The vacuum valve is provided with a valve main body including a valve body and a valve seat, and a drive portion which drives the valve body so as to open and close. The drive portion is provided with two pneumatic chambers. The valve body is driven by a balance between a pressure difference within the pneumatic chamber and a biasing force of a biasing spring. The control apparatus of the vacuum valve regulates a pneumatic pressure of one (pressure chamber) of the pneumatic chambers in accordance with a water level within the water storage basin, thereby controlling an opening and closing actuation of the vacuum valve.
The control apparatus of the vacuum valve includes a pneumatic type and a mechanical type. The pneumatic type regulates the pneumatic pressure of the pressure chamber in accordance with a pressure fluctuation corresponding to the water level within the water storage basin, which is detected by utilizing a diaphragm (e.g., see Patent Document 1). On the other hand, the mechanical type utilizes ascent and descent of a float in accordance with the water level within the water storage basin for regulating the pneumatic pressure of the pressure chamber. The mechanical type is superior in motion stability or the like as compared with the pneumatic type.
A vacuum type sewage line system to which the mechanism type control apparatus is applied is shown in FIG. 19. If a water level of waste water within a water storage basin 201 reaches a first water level HWL due to an inflow of the waste water from a natural falling pipe 200 connected to home sewage equipment, a control apparatus 203 opens a vacuum valve 204 in response to ascent of a float 202. Accordingly, a vacuum water supply pipe 205 connected to a vacuum station (not shown) is communicated with a water suction pipe 206. As a result, the waste water within the water storage basin 201 is drained to a downstream side via the vacuum water supply pipe 205. If the water level within the water storage basin 201 is drained to a second water level LWL, the control apparatus 203 closes the vacuum valve 204 in response to descent of the float 202. Accordingly, the communication between the vacuum water supply pipe 205 and the water suction pipe 206 is shut off, and the drainage is stopped.
The first water level HWL opening the vacuum valve 204 is set below an opening of the natural falling pipe 200. Accordingly, a backflow of the waste water from the natural falling pipe 200 to the home sewage equipment is prevented. Further, the second water level LWL closing the vacuum valve 204 is set above a lower end opening of the water suction pipe 206. Accordingly, the vacuum valve 204 is prevented from being maintained in the valve open state in a state where the water level is lower than a lower end of the water suction pipe 206. This is because a degree of vacuum of the vacuum water supply pipe 205 is lowered (pressure rises) due to mixture of air if a draining motion is continued in the state where the water level is below the lower end of the water suction pipe 206, thereby causing a reduction of a drainage capacity of the other vacuum valve unit connected to the same vacuum station, and a system failure.
However, the mechanical type control apparatus has the following problems.
First of all, as the apparatus is used, earth and sand mixed into the waste water is accumulated within the water storage basin 201. Further, at the time of newly constructing a system (unit), there is a case that a foreign material 207 such as a timber, a segment of a pipe, or the like is left within the water storage basin 201 due to carelessness of a worker. If the foreign material 207 is positioned at a lower portion of the float 202, it obstructs the descent of the float 202. In this case, since the vacuum valve 204 cannot be closed, it is impossible to stop the drainage.
Further, since the second water level LWL is set above the lower end of the water suction pipe 206, it is impossible to discharge a scum which is mixed into the waste water. The scum becomes hard in a region of the first water level HWL, and a surface area and a thickness are gradually increased with use. As a result, the float 202 is firmly fixed when it ascends to the first water level, and comes to a state in which it cannot descend. If the scum is peeled off from a wall surface of the water storage basin 201 by coming into contact with the float 202, and is positioned at a lower portion of the float 202, it obstructs the descent of the float 202. In such cases as well, it is impossible to close the vacuum valve 204, and the drainage cannot be stopped.
Patent Document 2 discloses a control apparatus of a vacuum valve which is provided with both functions of a mechanical type and a pneumatic type. The control apparatus is provided with first and second control mechanisms. The first control mechanism is a mechanism of a three-way valve structure which switches a pressure of a gas within a pressure chamber in conjunction with ascent and descent of a float. The second control mechanism is a control mechanism of a two-way valve structure which switches the pressure of the gas within the pressure chamber in conjunction with change of a degree of vacuum within the vacuum sewage pipe. In the control apparatus, the float type first control mechanism only carries out opening of the vacuum valve, and the differential type second control mechanism only carries out closing of the vacuum valve. In other words, if the waste water is reserved to a previously set water level within the water storage basin, the first control mechanism switches the vacuum valve from a valve closed state to a valve open state, and if the water level within the water storage basin becomes equal to or less than a lower end of the water suction pipe, the second control mechanism switches the vacuum valve from the valve open state to the valve closed state. Accordingly, it is possible to discharge the scum near the bottom of the water storage basin with the waste water. As mentioned above, the control apparatus of Patent Document 2 is superior as compared with the mechanical type control apparatus in that it can suppress the problem of malfunction of the float.
In the control apparatus of Patent Document 2, the first control mechanism for valve opening actuation and the second control mechanism for valve closing actuation are separate bodies. Therefore, in order to keep the vacuum valve, which is opened by the first control mechanism, in the valve open state until the second control mechanism executes the valve closing command, it is indispensable that a check valve is provided between the first control mechanism and the pressure chamber of the vacuum valve. That is, the check valve is further necessary in addition to two control mechanisms. Further, it is necessary to complicatedly arrange an air tube in a limited narrow space within the water storage basin. Specifically, it is necessary to connect the first and second control mechanisms respectively to the pressure chamber of the vacuum valve and the vacuum sewage pipe by an air tube. In these respects, the control apparatus of Patent Document 2 is complicated and large in its structure, and a high cost is required for manufacturing and installing.
Further, in the control apparatus of Patent Document 2, there may occur a phenomenon in which the vacuum valve repeats the valve opening and the valve closing in a short period of time, i.e., a chattering phenomenon. Specifically, if the float cannot descend due to the attachment of the foreign material such as the sediment and the remaining material, or the scum in the same manner as the mechanical type control apparatus in spite that the water level within the water storage basin is sufficiently lowered, there is a case that the first control mechanism comes to such a state where it keeps on outputting the valve opening command to the vacuum valve. In this case, even if the differential type second control mechanism outputs the valve closing command and the vacuum valve is closed, the vacuum valve is opened immediately by the valve opening command of the first control mechanism. As a result, the valve opening and the valve closing of the vacuum valve are repeated in an extremely short period of time. This chattering phenomenon also causes a reduction in draining capacity of the other vacuum valve unit connected to the same vacuum station, and a system failure.